This invention relates to the viewing of radiographs, particularly x-ray radiographs.

Conventionally x-ray radiographs are produced by illuminating an object with an x-ray source so that x-rays passing through the object strike a phosphor screen. The phosphor screen emits visible light when struck by x-rays and this emitted visible light is used to expose conventional white-light film. This film is then developed to produce an x-ray radiograph for normal viewing.

In order to examine the radiograph it is generally placed in front of a white-light light source and examined with the naked eye or using optical magnifiers. For some purposes, such as x-ray inspection of welds and castings to detect defects, this can be insufficiently sensitive and the eye is replaced by a video camera connected to a digital scanning and image storage processing and enhancement system. The processed and enhanced image is then displayed on a monitor. Although this increases the amount of detail that can be observed compared to the naked eye there is still a limit on the amount of detail which can be observed. Also the image storage processing and enhancement equipment is very expensive.

Another technique for improving the sensitivity of the examination with both naked eye and video viewing is to increase the light intensity used. This is limited by the heating effect on the radiograph which will distort as the very intense incident light heats it up and will eventually melt. It has been attempted to overcome this

problem by cooling the radiograph, for example by forced air cooling. However, there is still enough heating to cause sufficient distortion to make accurate measurements impossible.

_^ This invention was intended to overcome these drawbacks and to allow the amount of detail that can be observed in an x-ray radiograph to be increased.

In its broadest sense this invention comprises observing an x-ray radiograph using ultra-violet light having a spectrum matched to the transmission characteristics of the radiograph substrate.

This invention provides apparatus for viewing a radiograph comprising an ultra-violet light source, means including said light source for back-illuminating the radiograph, ultra-violet sensitive imaging means facing toward the light source, and disposed between them means for supporting the radiograph.

This ensures that a smaller proportion of the incident light is absorbed than in the prior art. As a result lower light intensities can be used, giving better resolution and sensitivity, without excessive heating of the radiographs.

The transmission spectrum of the radiograph is the transmission spectrum of the main body or substrate of the radiograph.

Preferably the light used is in the blue and ultraviolet regions, and most preferably it is in the ultra-violet region only.

An x-ray radiograph examination system embodyinσ the invention will be now be described by way of example

only with reference to the accompanying drawing in which:

Figure 1 shows diagrammatiσally an x-ray radiograph examination system employing the invention.

Figure 2 shows a similar x-ray radiograph examination system including a phosphorescent imaging screen.

Referring to the drawing an x-ray radiograph 1 is mounted in radiograph support means 2 which preferably comprises an X-Y manipulator 2. Ultra-violet light from an ultra-violet light source 3 passes through a diffuser screen 4 and back-illuminates the radiograph 1. On the opposite side of the radiograph 1 facing toward the light source 3 is an ultra-violet sensitive imaging means 5. In the embodiment illustrated imaging means 5 is a video camera having an ultra-violet sensitive video tube. Alternatively the imaging means might comprise a still camera loaded with film stock sensitive to ultra-violet light.

The light source 3, diffuser 4, manipulator 2, radiograph 1 and camera 5 are contained within a sealed enclosure 6 to prevent contamination by dust and dirt. The box 6 can be unsealed to allow the radiograph 1 to be exchanged for another.

The signals from the video camera 5 are connected to a signal processing and storage system 7 external to the sealed enclosure. The stored video image is viewable on visual display unit 8.

The X-Y manipulator 2 is capable of moving the radiograph 1 in directions perpendicular to the optical

axis of the imaging means 5. By moving the radiograph within the field of view of the camera 5 the whole of an otherwise larger radiograph 1 is able to be scanned and imaged by the camera 5 without sacrificing resolution.

The X-y manipulator 2 outputs a signal or signals on line 9 indicative of the position of the radiograph. Signal line 9 is connected to the signal processing and storage unit 7 which is adapted to correlate the position of the support means relative to a reference position with the image produced. The processing and storage unit 7 uses these signals to produce a display on the monitor 8 showing the X-Y coordinates on the radiograph 1 of the centre of the field of view of the camera 5. If an image of the radiograph 1 is stored by the processing and storage unit 7 the X-Y coordinates on the radiograph 1 of the centre of the field of view of the camera 5 are stored with the image to ensure that when the image is recalled later its position on the radiograph 1 will be known.

In general radiographs have a light transmission spectrum giving the highest coefficients of transmission in a frequency band extending from the ultra-violet region to the blue region.

As a result the use of ultra-violet light only is not essential, blue light could be used instead, however it has been found that the best results are obtained by using light having a range of frequencies from the blue to ultra-violet parts of the spectrum. A preferred band is that having wavelengths between 250 and 400 nanometers.

A light source 10 emitting light in a frequency band from blue into the ultra-violet may be used.

Accordingly camera 11 should have a video tube sensitive to this band of frequencies also. Whatever imaging medium is used in the imaging means 5, ie video tube, film stock etc, its sensitivity band should be matched to the emission spectrum of the illumination source 3.

Referring now to figure 2, there is shown x-ray an radiograph viewing system similar to that illustrated in figure 1 with the addition of a phosphorescent viewing screen placed between the radiograph 1 and the imaging means 5. For ease of reference like parts in both arrangements have been given like references.

The arrangement of figure 2 may permit a camera or film stock sensitive to, say, visible light to be used providing only that its response characteristic must match the radiation spectrum given out by the phosphorescent screen 12. Thus, for further example, a low light level camera may be used providing it matches the frequency spectrum of light emitted by the phosphorescent screen.

Although blue light only could be used it has been found advantageous to use ultra-violet light or a mixture of ultra-violet and blue light.

Although the ultra-violet and blue light is preferred for the radiographs used so far it is possible that other radiographs may have transmission characteristics such that other frequency bands are preferred.

The provision of a sealed box 6 around the optical apparatus is not essential but it is useful to prevent dust particles settling on the radiograph 1.

The use of a processing and storage unit 7 is not

essential, the image from the video camera 5 could be processed and then displayed directly on the visual display unit 8 in real time without any storage facilities being provided.

In both examples a still camera sensitive to the appropriate frequencies could be used instead of a video camera, with still photos being taken of areas of interest and later examined.